mosfet problems

[brian-i-bunker-u]

Ok so here is the situation

I have a Echo 1 AK700. The stock motor is a POS so I wanted to upgrade it. I purchased a systema turbo high speed motor. Upon installation I noticed my DIY mosfet getting really really hot. So hot that it promptly burnt it out. So I built a new one and tried it and noticed it would still get hot on semi but was ok on full auto. I checked my shimming, replaced gears with a fresh SHS 18:1, lubed etc. It still had the problem. So now I'm thinking that maybe the motor is bad or the spring is too heavy so I picked up a lonex A1.Popped it in and It is still having the problem. My last step has been to change out to 13:1 gears just to see what happens. I would have expected this to make it worse but no real change (maybe even slightly better).

The gun runs very smooth besides the overheating. It is also worth noting that the motor stays cool and so does that battery and wires. Im honestly at a loss here. The only other thing I can think of is that I got a bad batch of mosfet materials but I haven't had problems in my other guns so I don't think so.

Any ideas?

any good gun docs in the guelph area?

[pestobanana]

What FET are you using, and how are you wiring it in?

[EOD Steve]

Show us your schematic.

[brian-i-bunker-u]

this design

http://unconventional-airsoft.com/wp...ple-mosfet.jpg

[pestobanana]

That's the basic FET layout, how are you wiring it in to the gun?

[brian-i-bunker-u]

not sure what you mean by wire it into the gun? It was done just like the diagram. Its a version 3 gearbox so all wiring is external. I use 16AWG for the motor wires and 18 for the trigger leads.

[Kos-Mos]

Originally Posted by brian-i-bunker-u

not sure what you mean by wire it into the gun? It was done just like the diagram. Its a version 3 gearbox so all wiring is external. I use 16AWG for the motor wires and 18 for the trigger leads.

There should be 1 trigger lead, and you can use as small as 22ga wire for it. The other is a Y going battery +/motor +/trigger.

And there should be a resistor in-line with that 1 trigger lead, otherwise your MOSFET gets in triode mode and that sucks.

[brian-i-bunker-u]

My mosfet design is sound. I have used it in all my other guns and they work 100%.

[pestobanana]

If your MOSFET design and wiring were sound, you wouldn't be experiencing this issue. Can you show us a picture of the wiring?

[brian-i-bunker-u]

do you want a close up of the chip or just the wiring as a whole (need to know if I need to cut off my cover)

[pestobanana]

More interested in how you wired your gun as a whole, I'm going to assume the FET itself was assembled correctly.

[brian-i-bunker-u]

[pestobanana]

Well I guess the heat shrink is covering up the part I wanted to see.

So the FET is on the negative wire, which goes battery --> FET --> motor, then your positive wire goes straight from your battery to your motor. Your signal wires go from the FET --> trigger contacts --> battery positive?

[lurkingknight]

sound clip of the gun operating? Don't record in a tin can room either lol... if all you have is a shitty mic try and dampen the sound a bit by pulling a tshirt over the mic.

[brian-i-bunker-u]

Originally Posted by pestobanana

Well I guess the heat shrink is covering up the part I wanted to see.

So the FET is on the negative wire, which goes battery --> FET --> motor, then your positive wire goes straight from your battery to your motor. Your signal wires go from the FET --> trigger contacts --> battery positive?

thats correct